Osteoporosis has a significant impact on the population of the United States, with more than 10 million people affected by the disease and 24 million at risk. Osteoporosis is associated with decreased bone mass and deterioration of the trabecular architecture of the bone, which collectively impact the bone's mechanical properties. Often, this degenerative disease leads to bone fracture (2 million per year), with associated costs exceeding $16 billion annually. Traditionally, measurement of bone mineral density (BMD) has been the predominant diagnostic and screening tool for osteoporosis and other degenerative bone diseases.
Dual energy x-ray absorptiometry, or DXA, is the most popular current method of assessing bone density. In this method, a subject is exposed to low-dose x-rays having two distinct energy peaks, with different characteristics in soft tissue and bone. Subtraction of the soft tissue absorption allows quantification of BMD. The procedure is carried out while the subject is at rest, thus providing BMD data for the bone under static conditions.
However, structural failure of the human bone rarely occurs under static conditions. A better understanding of bone fracture and prevention requires measurement of the biomechanical properties of the bone when exposed to realistic, in vivo loading—that is, an assessment of “dynamic” bone quality.
The transmission, absorption and attenuation of energy that intakes to the skeleton due to heel strike is an important component of bone physiology and pathology. The human locomotion system, which consists of natural shock absorbers (joints with viscoelastic components, articular cartilage, meniscus, intervertebral disks, trabecular bone, etc.), is subjected to constant loading and impact not only during weight lifting activities but also during normal daily activities such as walking, running, stair-climbing, etc. During heel strike, the vertical force component acting on the foot is on the order of 1.5 times the body weight depending upon walking velocity. These force waves are gradually attenuated by the body's natural shock absorbers on their way toward the head. The process of force wave attenuation is the body's natural way of protecting the most vital organ, the brain.
Among all natural shock absorbers in the human body, the trabecular bone has the highest capacity (170 times higher than that of cartilage) to attenuate incoming shock waves associated with heel-strike during walking and running. Since osteoporosis is associated with decreased bone mass and deterioration of trabecular architecture of the bone, the disease detrimentally changes the bone's natural shock absorbing capacity. The need exists to develop non-invasive, economical tools for assessing and monitoring dynamic bone quality.
The present invention is directed to a computer system and method for quantifying bone shock absorption (BSA) under dynamic conditions in order to assess the dynamic bone quality in a subject. The BSA variable, bone damping (ζ), is a sensitive measure of the bone's structural integrity, a useful diagnostic of osteoporosis, and a valuable indicator of fracture risk.